Washington University in St. Louis SeniorCapstone Design Project

Abstract & Purpose

In the United States, buildings account for approximately 34% of total energy usage, and HVAC systems account for roughly half of that energy usage. Therefore, in order to accomplish the important goal of increasing energy efficiency and reducing energy usage in the United States, the usage of HVAC systems must become more efficient. An accurate room climate model that provides the true temperature of the room is needed when trying to increase the efficiency of HVAC systems. However, industry currently uses a very simple room climate model, a delayed first-order transfer function, to install HVAC systems and determine the temperature on a thermostat. Models using partial differential equations have been proven to be very accurate at modeling and determining temperatures. However, their high level of computational complexity means that it is not currently plausible to use them in commercial HVAC systems.

In conversations with my advisor and through literature research, I identified models that convert indoor thermal systems into electrical circuits as potentially being effective and with a low enough computational cost to be used commercially. In my project, I determine the equivalent electrical parameters from a thermal system. Then, using a simple two-room model, I test various scenarios and assumptions to determine the optimal conversion of a thermal system to an electrical circuit model. This model is then applied to a real apartment to test its accuracy. This test demonstrates the potential of this model to accurately predict temperatures and have the flexibility to adjust to changes in ambient and interior environments while serving as an useful diagnostic tool.